Feedback control device

ABSTRACT

In a feedback control apparatus comprising a controller, a control object to be controlled by the controller, and an observer for inputting a control output from the control object and an output of the controller and setting an output of a control object model to be a feedback signal, the observer includes an observer compensator for inputting a difference between the control output and an output of an element model and inputs, to the control object model, a sum of an output of the observer compensator and the output of the controller. Consequently, a control system having an excellent response performance can be constituted and a stable observer can easily be constituted.

TECHNICAL FIELD

[0001] The present invention relates to a feedback control method andapparatus in which a delay element is present in a controller or acontrol object or a dead time is present in the input and output of thecontrol object.

BACKGROUND ART

[0002] A dead time or a delay element of a filter is present in acontroller or a control object in most control systems such as a servoand a process control. FIG. 3 is a block diagram showing an ordinaryfeedback control system.

[0003] In FIG. 3, 2 denotes a main controller (for example, a PIDcontroller), 3 denotes a delay element of the controller, 4 denotes adelay element of a control object and 5 denotes an element having nodelay of the control object. In such a control system, the phase of thedelay element is delayed. Therefore, the gain of the controller cannotbe increased and a sufficient response characteristic cannot beobtained. For this reason, a compensation control for a phase delay isrequired.

[0004] In order to compensate for the phase delay, conventionally, aphase leading compensation element 12 is often added in series as shownin FIG. 4. If T_(a) and T_(b) are properly set to be T_(a)>T_(b), thephase of the phase leading compensation element 12 is led and the gainof the main controller 2 is increased so that a control performance canbe enhanced.

[0005] In the conventional phase compensation control method, however,there has been a problem in that a gain in the high-frequency region ofthe phase leading compensation element is increased and a high-frequencyoscillation is apt to be caused.

[0006] Moreover, a dead time is present in the inputs or outputs of mostcontrol systems such as a servo and a process control. FIG. 8 is a blockdiagram showing a conventional feedback control system. In FIG. 8, 22denotes an ordinary controller (for example, a PID controller) and 23denotes a control object including a dead time. In such a controlsystem, the phase of a dead time element is delayed. Therefore, the gainof the controller cannot be increased and a sufficient responsecharacteristic cannot be obtained. Therefore, it is necessary to carryout a compensation control for a dead time.

[0007] Conventionally, a Smith compensator shown in FIG. 9 has oftenbeen used to compensate for a dead time. In FIG. 9, 25 denotes aprediction model of a control object and 26 denotes a dead time element.Taking note of a control input and a feedback signal, a control systemin FIG. 9 can be equivalently rewritten as shown in FIG. 6. Referring toFIG. 6, the stability of a feedback system is the same as that of asystem having no dead time and the gain of a controller C(s) can beincreased so that a control output y can follow a target input r withhigh precision.

[0008] The disturbance removing characteristic of the conventional Smithmethod will be taken into consideration. Assuming that a disturbance dis present on a control input end as shown in FIG. 10, a transferfunction from the disturbance d to the control output y is given asfollows.

[0009] (1)

[0010] When the steady value of the control output y for a stepdisturbance d(s)=1/s is represented by Y_(sd), the following equationcan be obtained.

[0011] (2)

[0012] If C(s) has an integrator, the following equation can be set up.

[0013] (3)

[0014] If P(s) has a pole of s=0, Y_(sd)≠0 is obtained. Morespecifically, in the Smith method, there is a problem in that asteady-state deviation is made for a control object having the pole ofs=0. Moreover, if P(s) is unstable in the equation (1), there is aproblem in that an output diverges even if any small disturbance ismade.

[0015] It is an object of the invention to provide a control apparatuswhich can increase a control gain and has an excellent responsiveness.

[0016] It is another object of the invention to provide a feedbackcontrol apparatus capable of compensating for the phase delay of a delayelement so as not to make a high-frequency oscillation and causing acontrol output to follow a target input with high precision in a controlsystem in which a delay element is present in a controller or a controlobject.

[0017] It is a further object of the invention to provide a dead timecompensation feedback control apparatus capable of constituting a stablecontrol system for an unstable control object without making asteady-state deviation for a control object having a pole of s=0.

DISCLOSURE OF THE INVENTION

[0018] In order to attain the object, the invention provides a feedbackcontrol apparatus comprising a controller, a control object to becontrolled by the controller, and an observer for inputting a controloutput from the control object and an output of the controller andsetting an output of a control object model to be a feedback signal,wherein the observer includes an observer compensator for inputting adifference between the control output and an output of an element modeland inputs, to the control object model, a sum of an output of theobserver compensator and the output of the controller, and a controlapparatus for carrying out a feedback control to cause a control outputto follow a target input for a control system in which a delay elementis present in a controller or a control object, wherein an observer isconstituted in such a manner that a difference between the controloutput and an output of the observer is input to an observercompensator, an output of the observer compensator and an output of amain controller are added and input to an element model having no delayof the control object, and a signal obtained by sending an output of theelement model having no delay of the control object through a delayelement model of the controller and a delay element model of the controlobject is set to be the output of the observer, and the output of theelement model having no delay of the control object is subtracted fromthe target input and is input to the main controller, and a signalobtained by sending an output of the main controller through a delayelement of the controller is set to be a control input, therebycontrolling the control object. Moreover, the invention provides afeedback control apparatus for causing a control output to follow atarget input for a control object in which a dead time is present in aninput or an output, wherein an observer is constituted in such a mannerthat a difference between the control output and an output of a deadtime element of the control object is input to an observer compensator,an output of the observer compensator and a control input are added andinput to a prediction model of the control object, and an output of theprediction model of the control object is input to the dead time elementof the control object, and furthermore, is set to be a prediction valueof the control output, and the prediction value of the control output issubtracted from the target input and a value thus obtained is input to acontroller and an output of the controller is set to be the controlinput.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram showing the structural principle of afirst control system according to the invention,

[0020]FIG. 2 is an equivalent block diagram of FIG. 1,

[0021]FIG. 3 is a block diagram showing an ordinary feedback controlsystem,

[0022]FIG. 4 is a block diagram showing a conventional phase leadingcompensation control system,

[0023]FIG. 5 is a block diagram showing the structural principle of asecond control system according to the invention,

[0024]FIG. 6 is an equivalent block diagram of FIGS. 5 and 9,

[0025]FIG. 7 is a block diagram showing the case in which a disturbanceis taken into consideration in FIG. 5,

[0026]FIG. 8 is a block diagram showing a conventional feedback controlsystem,

[0027]FIG. 9 is a block diagram showing a control system using a Smithcompensator, and

[0028]FIG. 10 is a block diagram showing the case in which a disturbanceis taken into consideration in FIG. 9.

BEST MODE OF CARRYING OUT THE INVENTION

[0029] An embodiment of the invention will be described with referenceto the drawings. FIG. 1 is a block diagram showing the structuralprinciple of a control system according to the invention. In FIG. 1, 2denotes a main controller, 3 denotes a delay element of the controller,4 denotes a delay element of a control object, 5 denotes an elementhaving no delay of the control object, 7 denotes an element model havingno delay of the control object, 8 denotes a delay element model of thecontroller, 9 denotes a delay element model of the control object, and11 denotes an observer compensator.

[0030] In general, it is necessary to provide a filter in order toremove a noise when constituting the controller. In the control object,moreover, a dead time element or a primary delay element is present in acontrol input or a control output. If these delay elements are notseparated, it is hard to constitute the main controller in order tosimultaneously satisfy a stability and a control performance. Therefore,the controller is divided into the main controller 2 and the delayelement 3 of the controller and an observer including the delay elementof the controller is constituted based on an output u₁ of the maincontroller and a control output y, and an output having no delay of theobserver is set to be a feedback signal y_(f).

[0031] More specifically, the output u₁ of the main controller 2 and theoutput of the observer compensator 11 are added and input to the elementmodel 7 having no delay of the control object. The output of the elementmodel 7 having no delay of the control object is set to be the feedbacksignal y_(f) of the control system and a signal obtained by subtractingthe feedback signal y_(f) from a target input r through a subtracter 1is input to the main controller 2 and the output u₁ of the maincontroller 2 is input to the control object through the delay element 3of the controller, thereby controlling the control object, while it isinput to a subtracter 10 through the delay element model 8 of thecontroller and the delay element model 9 of the control object and asignal obtained by a subtraction is input from the control output y tothe observer compensator 11.

[0032] Referring to FIG. 1, in the open loop of the control system, atransfer function from the output u₁ of the main controller 2 to thefeedback signal y_(f) is obtained as follows.

[0033] (4)

[0034] Therefore, the control system in FIG. 1 can be rewrittenequivalently as shown in FIG. 2. Referring to FIG. 2, the stability of afeedback control system is the same as that of a system having no delayso that the gain of the main controller 2 can be increased. Moreover, atransfer function from the target input r to the control output y isobtained as follows.

[0035] (5)

[0036] Therefore, it is possible to cause the output y to follow thetarget input r with high precision by increasing the gain of the maincontroller 2.

[0037] Although an observer loop has a delay element, an input/outputcharacteristic is not related to the observer compensator 11 based onthe equation (5). For this reason, the gain of the observer compensator11 may be set to be low. Accordingly, a stable observer can easily beconstituted.

[0038] Another embodiment of the invention will be described withreference to the drawings. FIG. 5 is a block diagram showing thestructural principle of a second control system according to theinvention. In FIG. 5, 22 denotes a controller, 23 denotes a controlobject including a dead time, 25 denotes a prediction model of thecontrol object, 26 denotes a dead time element, and 28 denotes acompensator of an observer 20.

[0039] Referring to FIG. 5, a transfer function from a control input uto the feedback signal y_(f) is obtained as follows.

[0040] (6)

[0041] Therefore, the control system in FIG. 5 can be rewrittenequivalently as shown in FIG. 6. Referring to FIG. 5, the stability of afeedback system is the same as that of a system having no dead time sothat the gain of a controller C(s) can be increased. Moreover, atransfer function from the target input r to the control output y isobtained as follows.

[0042] (7)

[0043] Therefore, it is possible to cause the output y to follow thetarget input r with high precision by increasing the gain of thecontroller C(s).

[0044] In order to consider a disturbance removing characteristic, adisturbance d is given to a control input end as shown in FIG. 7.Referring to FIG. 7, a transfer function from the disturbance d to thecontrol output y is obtained as follows.

[0045] (8)

[0046] When the steady value of an output for a step disturbanced(s)=1/s is represented by Y_(sd), the following equation is obtained.

[0047] (9)

[0048] Both the controller C(s) and an observer compensator C_(o)(s)have integrators, the following equation is obtained.

Y_(sd)=0 (10)

[0049] More specifically, a steady-state deviation is not made for acontrol object having a pole of s=0. Referring to the equation (6),moreover, even if P(s) is unstable, an output does not diverge when C(s)stabilizes P(s) and C_(o)(s) stabilizes P(s)e^(−LS). Referring to theequation (7), the input/output characteristic is not related toC_(o)(s). Therefore, the gain of C_(o)(s) can be set to be low in such amanner that the P(s)e^(−LS) is stabilized.

[0050] As described above, in the invention, the observer including thedelay element of the controller is constituted and the output having nodelay of the observer is set to be the feedback signal so that thecontrol system is divided into a feedback control section and anobserver section. The stability of a feedback loop is the same as thatof a system having no delay and a control gain is increased.Consequently, the response performance of the control system can beenhanced. On the other hand, an observer loop has a delay element and anobserver compensator does not influence an input/output characteristic.Consequently, the gain of the observer compensator may be set to be low.Thus, a stable observer can easily be constituted.

[0051] In the invention, moreover, the observer of the dead time systemis constituted and the prediction value of the control output is set tobe the feedback signal. Consequently, the control system is divided intothe feedback control section and the observer section and the stabilityof the feedback loop is the same as that of a system having no dead timeand a control gain is increased. Consequently, the response performanceof the control system can be increased. In addition, since the observeris constituted, it is possible to obtain a high resistance to adisturbance as well as a stable object.

Industrial Applicability

[0052] According to the invention, a control system having an excellentresponse performance can be constituted and a stable observer can easilybe constituted.

1. A feedback control apparatus comprising a controller, a controlobject to be controlled by the controller, and an observer for inputtinga control output from the control object and an output of the controllerand setting an output of a control object model to be a feedback signal,wherein the observer includes an observer compensator for inputting adifference between the control output and an output of an element modeland inputs, to the control object model, a sum of an output of theobserver compensator and the output of the controller.
 2. A feedbackcontrol apparatus for carrying out a feedback control to cause a controloutput to follow a target input for a control system in which a delayelement is present in a controller or a control object, wherein anobserver is constituted in such a manner that a difference between thecontrol output and an output of the observer is input to an observercompensator 11, an output of the observer compensator 11 and an outputof a main controller 2 are added and input to an element model 7 havingno delay of the control object, and a signal obtained by sending anoutput of the element model 7 having no delay of the control objectthrough a delay element model 8 of the controller and a delay elementmodel 9 of the control object is set to be the output of the observer,and the output of the element model 7 having no delay of the controlobject is subtracted from the target input and is input to the maincontroller 2, and a signal obtained by sending an output of the maincontroller 2 through a delay element 3 of the controller is set to be acontrol input, thereby controlling the control object.
 3. A feedbackcontrol apparatus for causing a control output to follow a target inputfor a control object in which a dead time is present in an input or anoutput, wherein an observer is constituted in such a manner that adifference between the control output and an output of a dead timeelement of the control object is input to an observer compensator, anoutput of the observer compensator and a control input are added andinput to a prediction model of the control object, and an output of theprediction model of the control object is input to the dead time elementof the control object, and furthermore, is set to be a prediction valueof the control output, and the prediction value of the control output issubtracted from the target input and a value thus obtained is input to acontroller and an output of the controller is set to be the controlinput.